The offspring of a whale and a dolphin is a Wholphin.

 A wholphin or wolphin is an extremely rare hybrid born from a mating of a female bottlenose dolphin with a malefalse killer whale . The name implies a hybrid of whale and dolphin, although taxonomically, both are within the "oceanic dolphin" family, which is within the "toothed whale" suborder. The first recorded wholphin was born in a Tokyo SeaWorld, but he died after 200 days. The first wholphin in the United States and the first to survive was Kekaimalu, born at Sea Life Park in Hawaii on May 15, 1986; her name means "from the peaceful ocean". Although they have been reported to exist in the wild, only one is currently in captivity, at Sea Life Park in Hawaii.

 read more:- http://amazef.blogspot.in/2014/04/a-wholphin-actually-exists.html